1. Field of the Invention
Example embodiments relate generally to a system and method for controlling an operation of an application by forecasting a smoothed transport block size.
2. Related Art
FIG. 1 illustrates a conventional 3rd Generation Partnership Project Long-Term Evolution (3GPP LTE) network 10. The network 10 includes an Internet Protocol (IP) Connectivity Access Network (IP-CAN) 100 and an IP Packet Data Network (IP-PDN) 1001. The IP-CAN 100 generally includes: a serving gateway (SGW) 101; a packet data network (PDN) gateway (PGW) 103; a policy and charging rules function (PCRF) 106; a mobility management entity (MME) 108 and E-UTRAN Node B (eNB) 105 (i.e., base station, for the purposes herein the terms base station and eNB are used interchangeably). Although not shown, the IP-PDN 1001 portion of the EPS may include application or proxy servers, media servers, email servers, etc.
Within the IP-CAN 100, the eNB 105 is part of what is referred to as an Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (EUTRAN), and the portion of the IP-CAN 100 including the SGW 101, the PGW 103, the PCRF 106, and the MME 108 is referred to as an Evolved Packet Core (EPC). Although only a single eNB 105 is shown in FIG. 1, it should be understood that the EUTRAN may include any number of eNBs. Similarly, although only a single SGW, PGW and MME are shown in FIG. 1, it should be understood that the EPC may include any number of these core network elements.
The eNB 105 provides wireless resources and radio coverage for one or more user equipments (UEs) 110. That is to say, any number of UEs 110 may be connected (or attached) to the eNB 105. The eNB 105 is operatively coupled to the SGW 101 and the MME 108.
The SGW 101 routes and forwards user data packets, while also acting as the mobility anchor for the user plane during inter-eNB handovers of UEs. The SGW 101 also acts as the anchor for mobility between 3rd Generation Partnership Project Long-Term Evolution (3GPP LTE) and other 3GPP technologies. For idle UEs 110, the SGW 101 terminates the downlink data path and triggers paging when downlink data arrives for UEs 110.
The PGW 103 provides connectivity between UE 110 and the external packet data networks (e.g., the IP-PDN) by being the point of entry/exit of traffic for the UE 110. As is known, a given UE 110 may have simultaneous connectivity with more than one PGW 103 for accessing multiple PDNs.
The PGW 103 also performs policy enforcement, packet filtering for UEs 110, charging support, lawful interception and packet screening, each of which are well-known functions. The PGW 103 also acts as the anchor for mobility between 3GPP and non-3GPP technologies, such as Worldwide Interoperability for Microwave Access (WiMAX) and 3rd Generation Partnership Project 2 (3GPP2 (code division multiple access (CDMA) 1× and Enhanced Voice Data Optimized (EvDO)).
Still referring to FIG. 1, eNB 105 is also operatively coupled to the MME 108. The MME 108 is the control-node for the EUTRAN, and is responsible for idle mode UE 110 paging and tagging procedures including retransmissions. The MME 108 is also responsible for choosing a particular SGW for a UE during initial attachment of the UE to the network, and during intra-LTE handover involving Core Network (CN) node relocation. The MME 108 authenticates UEs 110 by interacting with a Home Subscriber Server (HSS), which is not shown in FIG. 1.
Non Access Stratum (NAS) signaling terminates at the MME 108, and is responsible for generation and allocation of temporary identities for UEs 110. The MME 108 also checks the authorization of a UE 110 to camp on a service provider's Public Land Mobile Network (PLMN), and enforces UE 110 roaming restrictions. The MME 108 is the termination point in the network for ciphering/integrity protection for NAS signaling, and handles security key management.
The MME 108 also provides control plane functionality for mobility between LTE and 2G/3G access networks with an interface from the SGSN (not shown) terminating at the MME 108.
The Policy and Charging Rules Function (PCRF) 106 is the entity that makes policy decisions and sets charging rules. It has access to subscriber databases and plays a role in the 3GPP architecture as specified in 3GPP TS 23.303 “Policy and Charging Control Architecture.”
Applicant server (AS) 102 is a server/node residing in IP-PDN 1001 that interfaces with UEs 110 in order to run applications on the UEs 110. AS 102 may for instance be a social networking website host, a service provider for online movies, etc.
FIG. 2 illustrates a conventional E-UTRAN Node B (eNB) 105. The eNB 105 includes: a memory 225; a processor 210; a scheduler 215; wireless communication interfaces 220; functions for MCS calculations 230 for each bearer; a transport-block size/modulation-and-coding-scheme/physical-resource-block (TMP) metrics 205 which accumulate the metrics from 215 and 210; and a backhaul interface 235. The processor 210 may also be referred to as a core network entity processing circuit, an EPC entity processing circuit, etc. The processor 210 controls the function of eNB 105 (as described herein), and is operatively coupled to the memory 225 and the communication interfaces 220.
The eNB 105 may include one or more cells or sectors serving UEs 110 within individual geometric coverage sector areas. Each cell individually may contain elements depicted in FIG. 2. Throughout this document the terms eNB, cell or sector shall be used interchangeably.
Still referring to FIG. 2, the communication interfaces 220 include various interfaces including one or more transmitters/receivers connected to one or more antennas to transmit/receive (wireline and/or wirelessly) control and data signals to/from UEs 110 or via a control plane or interface to other EPC network elements and/or RAN elements. Backhaul interface 235 is the portion of eNB 105 that interfaces with SGW 101 and MME 108 within IP-CAN 100. The scheduler 215 schedules control and data communications that are to be transmitted and received by the eNB 105 to and from UEs 110. The memory 225 may buffer and store data that is being transmitted and received to and from eNB 105.
Every Transmission Time Interval (TTI), typically equal to 1 millisecond, the scheduler 215 may allocate a certain number of Physical Resource Blocks (PRBs) to different bearers carrying data over the wireless link in the Downlink direction (i.e., transmitting from eNB 105 to UE 110) and Uplink direction (i.e., receiving data at eNB 105 from UE 110, which is received over backhaul 235). A “bearer” may be understood to be a link or channel used to exchange information to run application on the UE 110. The scheduler 215 may determine Modulation and Coding Schema (MCS) that may define how many bits of information per second per Hz may be packed into the allocated number of PRBs. The latter is defined by the 3GPP TS36.213 tables 7.1.7.1-1 and 7.1.7.2.1-1 (the contents of which is incorporated by reference in its entirety), where MCS is defined by a number between 0 and 28, where higher MCS values indicate that more bits may be allocated in a number of PRBs. The tables 7.1.7.1-1 and 7.1.7.2.1-1 include a lookup table for a number of bits of data that may be included in PRBs sent per TTI for a given allocated number of PRBs and a MCS value. MCS is computed by the scheduler using Channel Quality Indicator (CQI) values reported by the UE 110 that in turn may be derived from measured UE 110 wireless channel conditions in the form of Signal to Interference and Noise Ratio (SINR).
Scheduler 215 may make PRB allocation decisions based upon a Quality of Service (QoS) Class Identifier (QCI), which represents traffic priority hierarchy. There are nine QCI classes currently defined in LTE, with 1 representing highest priority and 9 representing the lowest priority. QCIs 1 to 4 are reserved for Guaranteed Bitrate (GBR) classes for which the scheduler maintains certain specific data flow QoS characteristics. QCIs 5 to 9 are reserved for various categories of Best Effort traffic.
Conventionally, the TMP metrics 205 may calculate appropriate transport block sizes (TBS) for data packets that are to be transmitted over wireless interface 220 towards UE in the downlink direction, by determining a number of physical resource blocks (PRBs) and an optimal modulation and coding scheme (MCS), as defined in a lookup table provided in standard 3GPP TS 36.213. However, due to the concavity of the 3GPP TS 36.213 lookup table, predictions in TBS values (when derived only from the look up table with predicted MCS and predicted PRBs input to the look up table) may be error prone. Furthermore, difficulty in accurately predicting TBS is caused by at least two additional reasons. First, knowing the MCS depends on channel quality information and a signal to noise ratio (SINR) for a bearer, while the number of PRBs depends on resource allocation strategies and various network state variables (e.g., the physical channel state, a traffic/data load and inter-cell interference level). The required TBS is therefore affected by all of the above-mentioned variables, in addition to fine-scale structures and rapid phenomena limitations. This means that a required TBS may vary significantly from time slot to time slot. Second, any noisy and/or inaccurate measurements or reports may increase the difficulty in arriving at a regression model for prediction.
Conventionally, the metrics of interest in determining TBS are determined using the following basic steps:
1. The UE receives a downlink transmission from an eNB.
2. The UE calculates an SINR for the received signal by way of embedded pilot tones in the received signal.
3. The UE calculates a Channel Quality Indicator (CQI) based on capacity calculations (for additive white Gaussian noise, or AWGN, channels, as an example) and reports the CQI to eNB.
4. The eNB receives the CQI and determines the SINR for the UE.
5. The eNB obtains a number of Physical Resource Blocks (PRBs) to be allocated to the UE in a next Transmission Time Index (TTI) by using the cell load in conjunction with an eNB scheduler algorithm.
6. The SINR calculated in (4) is used to select an appropriate Modulation Coding Scheme (MCS) for the UE for the next TTI. Thus MCS is strictly a channel quality driven metric.
7. The MCS and PRB calculated in (5) and (6) above are used to calculate an appropriate Transport Block Size (TBS) for transmission in the next TTI, by way of the lookup table of 3GPP TS 36.213.
Conventionally, there has been a significant amount of research involved in determining channel quality and/or link quality predictions. However, predicting appropriate future TBS values based on MCS and PRBs information has not been well-defined. Predicting accurate values for future TBS values may be used to better control an application level behavior especially with regard to video applications, and this type of prediction may also be used for other applications.